Conventionally, in high frequency circuits of communication terminals such as mobile phones or the like, surface acoustic wave (hereinafter, sometimes abbreviated as “SAW”) filters utilizing surface acoustic waves have been used. An SAW filter is used in a transmitting-use filter, receiving-use filter, duplexer, etc.
In recent years, SAW filters have been required to be increased in amount of attenuation, offer additional balance-unbalance conversion functions, and so on. The circuit configuration thereof is therefore becoming complicated as a general trend. In order to realize such a complex circuit, the technique of arranging lines so that lines having different potentials intersect with each other three-dimensionally is known (see for example Patent Literature 1, FIG. 9).
By employing such a three-dimensional line structure, a plurality of ground-use lines can be connected to a common ground terminal. Therefore, even an SAW filter having a complex circuit configuration can be reduced in size in its overall structure.
In the case of the conventional SAW filter explained above, however, an SAW element was easily influenced by spurious external electromagnetic waves and easily deteriorated in electrical characteristics. Further, the inductor component of the ground lines was apt to become larger. This also became a factor causing deterioration of the electrical characteristics.
The present invention was made in order to solve the above problem and provides an SAW filter and duplexer excellent in electrical characteristics.
Patent Literature 1: Japanese Patent Publication (A) No. 2007-142491